SPINAL
MUSCULAR ATROPHY (SMA) - TYPES 0 AND 1 |
ALTERNATE NAMES
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Prenatal onset arthrogryposis multiplex congenital (SMA0); Werdnig-Hoffman disease-Infantile
Muscular Atrophy (SMA1)
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DESCRIPTION
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Spinal Muscular Atrophy (SMA) of all types belongs to a group of hereditary diseases that cause weakness and wasting
of the voluntary muscles in the arms and legs of infants and children.
The disorders are caused by an abnormal or missing gene known as the survival motor
neuron gene (SMN1), which is responsible for the production of a protein essential
to motor neurons. Without this protein, lower motor neurons in the spinal cord degenerate
and die. The type of SMA is determined by the age of onset and the severity of symptoms.
Type 0 is prenatal. Type 1 (also known as Werdnig-Hoffman disease or infantile-onset
SMA) is evident at birth or within the first few months.
Symptoms include floppy limbs and trunk, feeble movements of the arms and legs, swallowing
difficulties, a weak sucking reflex, and impaired breathing. Legs tend to be more
impaired than arms.
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DIAGNOSTIC TESTING, PHYSICAL FINDINGS, AND ICD-9-CM/ICD-10-CM
CODING
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Diagnostic testing: The clinical evaluation includes a history and physical examination. Abnormalities
may be detected during the pregnancy, especially with onset of fetal movements. or
may reveal another affected family member. The history should define the onset of
the disease and its progression.
Physical findings: Physical symptoms may include:
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Muscle twitching and contractures;
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Labored breathing with use of accessory muscles; and
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Molecular testing of the SMN1 gene is needed for confirmation of diagnosis. Carrier
status must be defined before prenatal diagnosis is attempted.
ICD-9: 335.1
ICD-10: G12
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PROGRESSION
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The prognosis is poor for infants with SMA Types 0 and 1. SMA Type 0 infants never achieve any motor milestones and usually die between 2
and 6 months of age. SMA Type 1 children fare only slightly better in that they may
achieve sitting with support only and survive to 2 years or less without respiratory
assistance. SMA Type 1 children may survive longer if offered non-invasive respiratory
support (NIPPV or tracheotomy).
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TREATMENT
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There is no cure for SMA. There is no treatment for the progressive weakness caused
by the disease. Treatment consists of managing the symptoms and preventing complications.
Individuals with SMA Type 0 or 1 require little, if any, involvement of an orthopedist
due to their short life span. Supportive care is important. When nutrition/feeding
become concerns, tube feeding via nasogastric tube or gastrostomy may be offered.
Attention must be paid to the respiratory system, because affected people have difficulty
clearing secretions. Respiratory complications are common.
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SUGGESTED PROGRAMMATIC ASSESSMENT*
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Suggested MER for Evaluation: The diagnosis is confirmed by molecular genetic testing of the SMA1 gene. Homozygous
deletion of exon 7 of the SMN1 gene is seen in 95-98% of the cases while 2-5% of the
cases will have this deletion in one chromosome and an intragenic mutation of the
SMN1 gene in the other chromosome.
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Suggested Listings for Evaluation:
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DETERMINATION
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LISTING
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REMARKS
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Meets |
110.08 |
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111.22
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Genetically confirmed SMA0 or SMA1 |
Equals |
111.22 |
Pending genetic confirmation but with a clinical diagnosis of SMA0 or SMA1 |
* Adjudicators may, at their discretion, use the Medical Evidence of Record or the
listings suggested to evaluate the claim. However, the decision to allow or deny the
claim rests with the adjudicator.
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